Minnesota Power, a unit of Allete Inc, said the Boswell project is part of its long-term goal to diversify its energy mix to one-third renewable, one-third natural gas and one-third coal by the end of the next decade.

“We’ve made great strides in a relatively short amount of time to diversify our energy mix, going from 5 percent renewable and 95 percent coal in 2005 to a 20 percent renewable mix today,” Amy Rutledge, Minnesota Power spokeswoman, told Reuters on Wednesday.

The company hopes to start work on Boswell 4 after state regulators approve of an air permit. The unit entered service in 1980.

Minnesota Power increased the amount of renewable power it delivers to customers in part with the recent completion of its 292-MW Bison wind farm in North Dakota.

The company also expects to buy 250 MW of hydropower from Manitoba Hydro in Canada beginning in 2020, Rutledge said.

As for natural gas, Minnesota Power is seeking state approval to convert its 110-MW Laskin coal-fired power plant to burn natural gas in 2015, and Rutledge said the company is also evaluating a gas resource addition in the 2020 and beyond timeframe.

Minnesota Power provides electric service to 143,000 customers in northeast Minnesota.